Mutations and Cell Communication in Biology

Mutation

Permanent alteration in DNA sequence.

Somatic Mutation

Mutations passed to daughter cells in tissue.

Germline Mutation

Mutations passed to new organisms.

Wild Type

Non-mutated, normal gene expression.

Mutation Frequency

1 mistake per billion nucleotides in eukaryotes.

Proofreading

DNA repair mechanism with exonuclease activity.

Mismatch Repair System

Corrects mismatches in newly synthesized DNA.

Methyl Directed Mismatch Repair

Uses methylation to identify correct DNA strand.

Mut S

Scans DNA for mismatches.

Mut H

Cuts non-methylated strand for repair.

Mut L

Activates repair enzymes in mismatch repair.

Point Mutation

Change in a single base pair.

Frameshift Mutation

Inserts or deletes bases, altering reading frame.

Base Substitution

Replacement of one nucleotide with another.

Transition

Base substitution within the same nucleotide family.

Transversion

Base substitution between different nucleotide families.

Nonsense Mutation

Creates a premature stop codon.

Missense Mutation

Changes one amino acid in the protein.

Frameshift Effects

Alters downstream amino acid sequence.

Cytoskeleton

Dynamic protein fiber system for cell support.

Actin

Globular protein forming microfilaments.

Microtubules

Hollow tubes made of tubulin dimers.

Intermediate Filaments

Provide structural support, 8-12 nm in size.

Nucleation

Initial step in actin filament formation.

G Actin

Monomeric form of actin.

F Actin

Polymeric form of actin filaments.

Capping Proteins

Regulate actin filament growth.

Myosin

Motor protein converting ATP to mechanical energy.

Microtubule Organizing Centers

Structures where microtubules originate.

Centrosome

Primary MTOC, contains centrioles.

Dynein

Motor protein moving toward minus end of MT.

Kinesin

Motor protein moving toward plus end of MT.

Cell Cycle

Series of phases leading to cell division.

M Phase

Phase of mitosis and cytokinesis.

Interphase

Preparation phase before cell division.

Late Prophase

Nucleus disassembles, forming nuclear membrane vesicles.

Nuclear Lamina

Intermediate filament providing structural support to nucleus.

Telophase

Reassembly of nucleus and chromosome decondensation.

Kinetochores

Protein complexes attached to centromeres of chromatids.

Microtubule Types

Includes kinetochore, polar, and astral microtubules.

Anaphase A

Sister chromatids move to opposite poles.

Anaphase B

Spindle poles move apart, separating sister chromatids.

Cytokinesis

Division of cytoplasm, forming two daughter cells.

Co-translational Sorting

Proteins sent to ER during synthesis.

Post-translational Sorting

Proteins sorted after complete synthesis.

Nuclear Pore Complex

Facilitates transport of proteins into nucleus.

Molecular Weight Thresholds

MW < 20 kDa passively diffuses; > 60 kDa requires energy.

Nuclear Localization Signal (NLS)

Basic amino acid-rich signal for nuclear import.

Nuclear Export Signal (NES)

Leucine-rich signal keeping proteins out of nucleus.

Importin

Protein that transports NLS-containing proteins into nucleus.

RanGTP

Binds importin, facilitating cargo release in nucleus.

Exportin

Recognizes NES for exporting proteins from nucleus.

Mitochondrial Genome

Contains 13 protein-coding genes, 22 tRNAs.

Mitochondrial Protein Import

Involves TOM, TIM, and chaperones for proper folding.

RER Protein Import

SRP pauses translation for ER targeting.

Endomembrane System

Pathway: RER → Golgi → vesicles → plasma membrane.

Cell Communication Types

Includes direct, contact-dependent, autocrine, paracrine, endocrine.

Receptor Activation

First stage in cellular response to signals.

Dissociation Constant (Kd)

Indicator of receptor-ligand binding affinity.

Allosteric Interaction

Binding alters receptor activity, triggering response.

EGF Pathway

Signal transduction pathway promoting cell growth.

GCPR Mechanism

Ligand binding activates G protein signaling cascade.

Activated Subunits

Promote cellular responses via signaling molecules.

G Protein

Molecular switch; active with GTP, inactive with GDP.

cAMP

Second messenger synthesized from ATP by adenylyl cyclase.

PKA

Protein kinase activated by cAMP; phosphorylates proteins.

Epinephrine Pathway

Stimulates glycogen breakdown via PKA activation.

Glycogen Synthase

Enzyme inhibited by PKA to stop glycogen storage.

Phosphorylase Kinase

Activated by PKA to stimulate glycogen breakdown.

Amplification

One epinephrine molecule triggers 100 million glycogen molecules.

Crosstalk

Interaction between signaling pathways, enhancing or inhibiting effects.

Apoptosis

Programmed cell death for tissue sculpting and maintenance.

Extrinsic Apoptosis

Triggered by death receptor aggregation and DISC formation.

Intrinsic Apoptosis

Activated by DNA damage, involving cytochrome c release.

p53

Tumor suppressor protein regulating cell cycle and apoptosis.

ncRNA

Non-coding RNA involved in gene regulation and function.

Scaffold

Framework for assembling protein complexes in ncRNA.

Ribozyme

RNA with catalytic activity due to folding.

RNAi

RNA interference mechanism for gene silencing.

siRNA

Small interfering RNA; perfect match to target mRNA.

miRNA

MicroRNA; imperfect match, regulates gene expression.

HOTAIR

ncRNA regulating HOX genes via histone modification.

CRISPR-Cas System

Bacterial defense mechanism against viruses.

Adaptation Phase

Cas proteins incorporate phage DNA into CRISPR locus.

Expression Phase

Transcription of pre-crRNA and tracrRNA for defense.

tracrRNA

Guides pre-crRNA in CRISPR-Cas system assembly.